This invention relates to chairs which provide for discharging the electrostatic charge of an occupant of the chair, which chairs are sometimes referred to as antistatic chairs or static protective chairs.
The electrically conductive chairs are widely used in offices and in factories where it is desirable to avoid build-up of electrostatic charge on the person who is occupying the chair. Many chairs used in such situations provide for rotation of the seat relative to the support base and for raising and lowering of the seat relative to the support base. It is desirable to provide an electrically conductive path from the seat and/or back of the chair to the floor on which the chair rests while also permitting rotation and raising and lowering of the seat relative to the base. A number of designs have been proposed for such a product, and three are shown in U.S. Pat. Nos. 4,513,347; 4,625,257; and 4,747,011. In the electrical conductive chair, it is usually desirable to incorporate an electrical resistance in the electrical path between the seat and the floor and this is accomplished by inserting a resistor, typically a one megohm resistor, in series in the electrical path.
Previous arrangements have been utilized for installing the resistor. By way of example, in U.S. Pat. No. 4,513,347 the resistor is in installed in a plastic sleeve and carried in a plastic shell attached to the chair. In U.S. Pat. No. 4,625,257 the resistor is mounted in an insulating sleeve projecting downward from the seatpost of the chair, with a conducting chain hanging from the resistor or from a zener breakdown device attached to the resistor. In U.S. Pat. No. 4,747,011 two resistors are mounted in a spacer between a base flange and a thrust bearing, with the leads of the resistors on the upper and lower surfaces of the spacer for contacting the thrust bearing and base flange.
There have been problems with stability and reliability and operating life of these prior arrangements, and it is an object of the present invention to provide an electrically conductive chair with a new and improved arrangement for installing an electrical resistance in the electrical conductive path between the chair seat and floor. One problem has been with breaking of the leads of the resistors used in providing the desired electrical resistance.
Other objects, advantages, features and results will more fully appear in the course of the following description.